Flexographic printing involves, among other things, the use of rapid drying, liquid inks which are applied to webs of paper stock by a plate roll having a raised surface bearing against an impression roll which backs up the web. As a result of the fast-drying characteristics of the liquid inks used in this art, a "central impression" type of flexographic press can be provided which utilizes a relatively large diameter impression roll about which is positioned a series of print stations, each including its own plate roll for applying an image to the web as it is advanced around the common impression roll for all of the stations. In this manner several different colors can be printed in rapid succession whereupon other operations such as die cutting and/or coating and curing the printed material with a protective finish may be performed, all without the risk of smearing the inks or otherwise damaging the finished product. "In-line" presses having an impression roll for each print station are also available.
It is not uncommon for presently available flexographic presses to be provided with three print stations so as to permit three-color printing. However, in order to obtain four-color capability, it is typically necessary to acquire a much larger press, whether "central impression" or "in-line", that is considerably more expensive and complex mechanically, therefore placing four-color capability out of the reach of many small operators unable to afford the capital costs involved in such larger machines. Moreover, even in the more expensive central impression machines, it has not heretofore been possible to achieve backside printing of the web, and in the in-line machines, that special feature is only available if a costly turnbar assembly is employed between a pair of the print stations to flip over the web as it passes from one station to the next. Turnbars, while adequately serving the purpose of presenting the opposite side for printing, also introduce a number of undesirable factors which make their use not particularly attractive.